Semiconductor light-emitting element

ABSTRACT

Part of light emitted downward by an active layer is reflected by an electrode functioning as a reflective layer, and travels upward to radiate outside. Since the electrode is made of a metal, it reflects almost all light regardless of its incident angle, and light can be efficiently extracted.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor light-emitting element.

In recent years, semiconductor light-emitting elements are widely usedin an outdoor display, automobile indicator, and the like. Thesemiconductor light-emitting element is a device using emissionrecombination of electrons and holes injected in a p-n junction region.Emission ranging from infrared radiation to ultraviolet radiation can berealized by changing the semiconductor material of a light-emittinglayer.

FIG. 30 shows the structure of a conventional semiconductorlight-emitting element. An n-type GaAs buffer layer 3202, an n-type DBR(Distributed Bragg Reflector) reflective layer 3203 made of InGaAlP andGaAs to reflect light using the Bragg reflection effect, an n-typeInGaAlP cladding layer 3204, an active layer 3205, a p-type InGaAlPcladding layer 3206, a p-type AlGaAs window layer 3207, and a p-typeGaAs contact layer 3208 are sequentially formed on the upper surface ofan n-type GaAs substrate 3201.

An n-type electrode 3209 is formed on the lower surface of the n-typeGaAs substrate 3201, and a p-type electrode 3210 is formed on the p-typeGaAs contact layer 3208. Power is supplied to the light-emitting elementto emit light from the active layer 3205. Light emitted downward in FIG.30 by the active layer 3205 is reflected by the reflective layer 3203,and radiated to above the element via the window layer 3207 togetherwith the light emitted upward.

The conventional semiconductor light-emitting element suffers thefollowing problem.

Part of light that is emitted downward by the active layer 3205 andtravels straight toward the reflective layer 3203 is reflected by thereflective layer 3203 without being absorbed by the substrate 3201, andcan be effectively extracted outside.

However, the reflective layer 3203 exhibits a very low reflectivity withrespect to light traveling diagonally toward the reflective layer 3203,so not all the light from the active layer 3205 can be extractedoutside.

The semiconductor light-emitting element absorbs light by a substratewhich provides a critical angle defined by the difference in refractiveindex between the semiconductor crystal and the atmosphere or enablescrystal growth. For this reason, light which can be extracted outside isonly several % of internally emitted light.

FIG. 26 shows the structure of another semiconductor light-emittingelement relating to the present invention.

A multilayered reflective film 1001, p-type contact layer 1002, p-typecladding layer 1003, active layer 1004 functioning as a light-emittinglayer, n-type cladding layer 1005, and n-type contact layer 1006 areformed on a p-type semiconductor substrate 1000. An n-type electrode1007 is formed on the contact layer 1002, whereas a p-type electrode1008 is formed on the contact layer 1006.

Part of light emitted by the active layer 1004 that travels toward then-type cladding layer 1005 is extracted outside via the cladding layer1005.

Light that travels toward the p-type cladding layer 1003 is reflected bythe multilayered reflective film 1001, and extracted outside via then-type cladding layer 1005.

In this structure, light emitted toward the substrate 1000 can bereflected by the reflective film 1001, and extracted outside.

However, the reflectivity of light which is not vertically incident onthe reflective film 1001 is low, the electrodes 1007 and 1008 whichshield light exist on the light extraction surface, and the active layer1004 is formed on the reflective film 1001. This results in lowcrystallinity and short service life.

FIG. 27 shows still another semiconductor light-emitting elementrelating to the present invention. An n-type InGaP buffer layer 1102,n-type InAlP cladding layer 1103, InGaAlP active layer 1104 functioningas a light-emitting layer, p-type InAlP cladding layer 1105, and p-typeGaAs contact layer 1106 are formed on the upper surface of an n-type GaPsubstrate 1101. A p-type electrode 1107 is formed on the p-type GaAscontact layer 1106, while an n-type electrode 1100 is formed on thelower surface of the substrate 1101.

Light emitted by the InGaAlP active layer 1104 is reflected by the n-and p-type electrodes 1100 and 1107, and extracted outside from a regionof the contact layer 1106 which is not shielded by the p-type electrode1107.

In this structure, however, light concentrated immediately below theelectrode 1107 is shielded by the electrode 1107, and cannot beextracted outside.

In the element shown in FIG. 27, only several % of light emitted by theactive layer 1104 can be extracted outside owing to the difference inrefractive index between the crystal and the air.

As the semiconductor light-emitting element, a compound semiconductorlight-emitting element using a GaAs-based semiconductor material isadopted to emit light ranging from red to green, and a galliumnitride-based compound semiconductor light-emitting element usingAl(x)Ga(y)In(1−x−y)N (0≦x, y≦1, x+y≦1) is adopted to emit light from theultraviolet range to the blue/green range.

However, the refractive indices of these light-emitting elements arehigh (GaN=2.67, GaAs=3.62), their critical angles are small (GaN=21.9°,GaAs=16.0°), and thus their light extraction efficiencies are low.

The GaAs system exhibits large light absorption on the substrate.Emitted light is absorbed by the substrate to decrease the lightextraction efficiency.

FIG. 29 shows still another semiconductor light-emitting elementrelating to the present invention.

An n-type GaAs buffer layer 1301, n-type InGaAlP cladding layer 1302,InGaAlP active layer 1303, p-type InGaAlP cladding layer 1304, andp-type AlGaAs current diffusion layer 1305 are sequentially grown on theupper surface of an n-type GaAs substrate 1300. A p-side electrode pad1307 is formed on the p-type AlGaAs current diffusion layer 1305,whereas an n-side electrode 1306 is formed on the lower surface of then-type GaAs substrate 1300.

In this structure, a current flowing from the p-side electrode 1307 iswidened by the p-type AlGaAs current diffusion layer 1305, and injectedfrom the p-type InGaAlP cladding layer 1304 to the InGaAlP active layer1303. The light is extracted outside the element via the p-type AlGaAscurrent diffusion layer 1305.

In the GaAs-based compound semiconductor light-emitting element havingthis structure, part of light emitted by the active layer 1303 thattravels toward the substrate 1300 is absorbed by the substrate 1300, andcannot be extracted outside the element. More specifically, 50% of theemitted light cannot be extracted, which is fatal to high luminance.

As described above, the elements relating to the present inventionsuffer low light extraction efficiency.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its object to provide a semiconductorlight-emitting element capable of efficiently extracting light emittedby a light-emitting layer outside the element.

According to the present invention, there is provided a semiconductorlight-emitting element comprising a substrate, a reflective layer whichis formed on the substrate, contains a metal, and reflects light, alight-emitting layer formed on the reflective layer to emit light, and atransparent electrode formed on the light-emitting layer to transmitlight.

The light-emitting layer desirably has a double-heterostructure in whichan active layer is sandwiched between first and second cladding layers.

The semiconductor light-emitting element can further comprise anelectrode of one conductivity type between a surface of the substrateand the reflective layer, a contact layer of the one conductivity typebetween the reflective layer and the light-emitting layer, and a contactlayer of an opposite conductivity type between the light-emitting layerand the transparent electrode.

The semiconductor light-emitting element can further comprise anelectrode of one conductivity type between a surface of the substrateand the reflective layer, a contact layer of the one conductivity typebetween the reflective layer and the light-emitting layer, and a contactlayer of an opposite conductivity type between the light-emitting layerand the transparent electrode.

The semiconductor light-emitting element can further comprise a strainrelaxing layer which is sandwiched between the contact layer of oneconductivity type and the first cladding layer, and has a middle bandgap between band gaps of the contact layer of the one conductivity typeand the first cladding layer.

The contact layer of the one conductivity type and the contact layer ofthe opposite conductivity type may contain InGaP or InGaAlP.

The semiconductor light-emitting element can further comprise anintermediate layer between the electrode of the one conductivity typeand the reflective layer.

The reflective layer may have a two-layered structure made up of atransparent conductive film and a metal.

The transparent electrode may be formed using an ITO film.

If the substrate contains a metal, preferable heat dissipation can beattained.

Compositions of first and second cladding layers are desirably adjustedto set band gaps of the first and second cladding layers to be largerthan a band gap of an active layer.

An active layer may have a single or multiple quantum well structureincluding a well layer and a barrier layer.

According to the present invention, the reflective layer made of a metalcan obtain a high reflectivity regardless of the angle of incident lighton the reflective layer. Light emitted inside the element can beefficiently extracted outside.

A semiconductor light-emitting element according to the presentinvention comprises a transparent semiconductor substrate, a bufferlayer formed on the semiconductor substrate and lattice-matched with thesemiconductor substrate, a light-emitting layer formed on the bufferlayer, a first electrode formed on the buffer layer, and a secondlight-reflecting electrode formed on the light-emitting layer.

According to the present invention, light is extracted from thetransparent substrate to increase the light extraction efficiency andluminance. The buffer layer lattice-matched with the substrate canprolong the service life with high crystallinity.

A semiconductor light-emitting element according to the presentinvention comprises a semiconductor substrate, a light-emitting layerformed on the semiconductor substrate, and first and second electrodesformed on the same plane, wherein the semiconductor substrate has alight extraction window so as to pass light emitted by thelight-emitting layer.

The first and second electrodes are formed on the same plane. One ofthese electrodes can be directly formed on a heat sink to increase theluminance without saturating a light output up to a large current.

A semiconductor light-emitting element manufacturing method according tothe present invention comprises the steps of forming a buffer layer on atransparent semiconductor substrate so as to be lattice-matched with thesemiconductor substrate, sequentially forming a first contact layer, afirst cladding layer, a light-emitting layer, a second cladding layer,and a second contact layer on the buffer layer, partially removing thefirst cladding layer, the light-emitting layer, the second claddinglayer, and the second contact layer to expose a surface of the firstcontact layer, forming a first electrode on the exposed surface of thefirst contact layer, and forming a second light-reflecting electrode ona surface of the second contact layer.

A semiconductor light-emitting element manufacturing method according tothe present invention comprises the steps of sequentially forming abuffer layer, a first contact layer, a first cladding layer, alight-emitting layer, a second cladding layer, and a second contactlayer on a semiconductor substrate, partially removing the firstcladding layer, the light-emitting layer, the second cladding layer, andthe second contact layer to expose a surface of the first contact layer,forming a first electrode on the exposed surface of the first contactlayer, forming a second light-reflecting electrode on a surface of thesecond contact layer, and forming a light extraction window at a portionof the semiconductor substrate at which the light extraction windowfaces the second electrode.

A semiconductor light-emitting element according to the presentinvention comprises a transparent semiconductor substrate, adouble-heterostructure which is formed on the semiconductor substrateand contains a light-emitting layer and first and second cladding layersthat sandwich two surfaces of the light-emitting layer, and a contactlayer which is formed on the double-heterostructure and has a recessedsurface.

Since the recessed region is set on the contact layer formed on thetransparent substrate, light from the light-emitting layer can bereflected to the side surface or the like, and effectively extractedoutside the element. Thus, the light extraction efficiency increases.

A semiconductor light-emitting element manufacturing method according tothe present invention comprises the steps of sequentially forming abuffer layer, a first cladding layer, a light-emitting layer, a secondcladding layer, and a contact layer on a transparent semiconductorsubstrate, recessing a surface of the contact layer, forming a firstlight-reflecting electrode on the surface of the contact layer, andforming a second electrode on a surface of the semiconductor substrateso as to remove a portion at which the second electrode faces the firstelectrode.

Alternatively, a semiconductor light-emitting element manufacturingmethod according to the present invention comprises the steps of forminga buffer layer on a transparent semiconductor substrate so as to belattice-matched with the semiconductor substrate, sequentially forming afirst cladding layer, a light-emitting layer, a second cladding layer,and a contact layer on the buffer layer, recessing a surface of thecontact layer, forming a first light-reflecting electrode on the surfaceof the contact layer, and forming a second electrode on a surface of thesemiconductor substrate.

A semiconductor light-emitting element according to the presentinvention comprises at least a light-emitting layer formed on asemiconductor substrate, wherein a shape of the semiconductorlight-emitting element is a polygonal prism having at least five cornersor a circular cylinder.

Since the element shape is a polygonal prism or circular cylinder, lightreflected by the end face is reduced, compared to a quadrangular prism.Light inside the element can be effectively extracted outside from theend face to increase the light extraction efficiency.

A semiconductor light-emitting element according to the presentinvention having a light-emitting layer for emitting light in adirection of plane comprises a photonics crystal layer on at least onesurface of the light-emitting layer.

The photonics crystal layer may be formed on the light-emitting layer ona side of a compound semiconductor light-emitting element opposite to alight extraction surface.

Alternatively, the photonics crystal layer may be formed on thelight-emitting layer on a light extraction surface side of thesemiconductor light-emitting element, and a through dislocation mayexist on the light extraction surface in a substantially verticaldirection to pass light emitted by the light-emitting layer.

A semiconductor light-emitting element according to the presentinvention comprises a semiconductor substrate, a contact layer formed onthe semiconductor substrate, a first cladding layer formed on thecontact layer, a light-emitting layer formed on the first claddinglayer, and a second cladding layer formed on the light-emitting layer,wherein an interface of the contact layer in contact with the firstcladding layer is corrugated to have a gradient index, and light emittedby the light-emitting layer is reflected by the interface.

A semiconductor light-emitting element according to the presentinvention comprises a semiconductor substrate, and a light-emittinglayer formed on the semiconductor substrate, wherein the semiconductorsubstrate has a rounded edge.

Alternatively, a semiconductor light-emitting element according to thepresent invention comprises a photonics crystal layer, and at least onelight-emitting element formed on each of two surfaces of the photonicscrystal layer, wherein the light-emitting elements emit light withdifferent emission wavelengths.

A semiconductor light-emitting element according to the presentinvention comprises a transparent semiconductor substrate, a Braggreflective layer formed on the semiconductor substrate, an active layerformed on the Bragg reflective layer, and a photonics crystal layerformed on the active layer.

A semiconductor light-emitting element manufacturing method according tothe present invention comprises the steps of sequentially forming abuffer layer, a first cladding layer, a light-emitting layer, and asecond cladding layer on a first semiconductor substrate, forming aphotonics crystal layer on the second semiconductor substrate, fusingthe second cladding layer and the photonics crystal layer, and removingthe first semiconductor substrate and the buffer layer.

Alternatively, a semiconductor light-emitting element manufacturingmethod according to the present invention comprises the steps ofsequentially forming a buffer layer, a contact layer, a first claddinglayer, a light-emitting layer, and a second cladding layer on a firsttransparent semiconductor substrate, forming a photonics crystal layeron a second semiconductor substrate, fusing the first semiconductorsubstrate and the photonics crystal layer, and removing the secondsemiconductor substrate, wherein the photonics crystal layer contains athrough dislocation on a light extraction surface in a substantiallyvertical direction to pass light emitted by the light-emitting layer.

Alternatively, a semiconductor light-emitting element manufacturingmethod according to the present invention comprises the steps of forminga contact layer on a semiconductor substrate, corrugating a surface ofthe contact layer, and sequentially forming a first cladding layer, alight-emitting layer, and a second cladding layer on the contact layer,wherein a gradient index is given by the corrugated interface of thecontact layer in contact with the first cladding layer, and lightemitted by the light-emitting layer is reflected by the interface.

A semiconductor light-emitting element manufacturing method according tothe present invention comprises the steps of forming at least alight-emitting layer on a semiconductor substrate, and processing anedge of the semiconductor substrate to round the edge.

A semiconductor light-emitting element manufacturing method according tothe present invention comprises the steps of forming a buffer layer on afirst transparent semiconductor substrate, forming a Bragg reflectivelayer on the buffer layer, sequentially forming a light-emitting layer,a cladding layer, and a bonding layer on the Bragg reflective layer,forming a photonics crystal layer on a second semiconductor substrate,bonding the cladding layer and the photonics crystal layer via thebonding layer, and removing the second semiconductor substrate.

A region having a gradient index inside the photonics crystal layer orsemiconductor layer is formed on one surface of the light-emittinglayer. Thus, light emitted by the light-emitting layer can beefficiently extracted outside the element to increase the extractionefficiency and luminance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the first embodimentof the present invention;

FIG. 2 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the second embodimentof the present invention;

FIG. 3 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the third embodimentof the present invention;

FIG. 4 is a longitudinal sectional view showing the longitudinal sectionof an element in one step of a semiconductor light-emitting elementmanufacturing method according to the fourth embodiment of the presentinvention;

FIG. 5 is a longitudinal sectional view showing the longitudinal sectionof the element in a step subsequent to the step shown in FIG. 4 in thesemiconductor light-emitting element manufacturing method;

FIG. 6 is a longitudinal sectional view showing the longitudinal sectionof the element in a step subsequent to the step shown in FIG. 5 in thesemiconductor light-emitting element manufacturing method;

FIG. 7 is a longitudinal sectional view showing the longitudinal sectionof the element in a step subsequent to the step shown in FIG. 6 in thesemiconductor light-emitting element manufacturing method;

FIG. 8 is a longitudinal sectional view showing the longitudinal sectionof the element in a step subsequent to the step shown in FIG. 7 in thesemiconductor light-emitting element manufacturing method;

FIG. 9 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the fifth embodimentof the present invention;

FIG. 10 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the sixth embodimentof the present invention;

FIG. 11 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the seventh embodimentof the present invention;

FIG. 12 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the eighth embodimentof the present invention;

FIG. 13 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the ninth embodimentof the present invention;

FIG. 14 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the tenth embodimentof the present invention;

FIG. 15 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the eleventhembodiment of the present invention;

FIG. 16 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the twelfth embodimentof the present invention;

FIG. 17 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the thirteenthembodiment of the present invention;

FIG. 18 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the fourteenthembodiment of the present invention;

FIG. 19 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the fifteenthembodiment of the present invention;

FIG. 20 is a longitudinal sectional view showing the method for forminga roughness on the surface of the GaN layer of the semiconductorlight-emitting element according to the fiftennth embodiment of thepresent invention;

FIG. 21 is a longitudinal sectional view showing the another method forforming a roughness on the surface of the GaN layer of the semiconductorlight-emitting element according to the fifteenth embodiment of thepresent invention;

FIG. 22 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the sixteenthembodiment of the present invention;

FIG. 23 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the seventeenthembodiment of the present invention;

FIG. 24 is a longitudinal sectional view showing the structure of asemiconductor light-emitting element according to the eighteenthembodiment of the present invention;

FIG. 25 is a longitudinal sectional view showing the procedure of themethod for manufacturing a photonics crystal using GaN;

FIG. 26 is a longitudinal sectional view showing the structure of aconventional semiconductor light-emitting element;

FIG. 27 is a longitudinal sectional view showing the structure ofanother conventional semiconductor light-emitting element;

FIG. 28 is a longitudinal sectional view showing the procedure of themethod for manufacturing a photonics crystal using GaAs;

FIG. 29 is a longitudinal sectional view showing the structure of afurther other conventional semiconductor light-emitting element;

FIG. 30 is a longitudinal sectional view showing the structure of afurther other conventional semiconductor light-emitting element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

(1) The First Embodiment

FIG. 1 shows the structure of a semiconductor light-emitting elementaccording to the first embodiment of the present invention.

P-type Au/Zn electrodes 3102 and 3103, a p-type GaAs contact layer 3104,a p-type cladding layer 3105 made of In(x′)Ga(y′)Al(1−x′−y′)P, an activelayer 3106 made of In(x″)Ga(y″)Al(1−x″−y″)P, an n-type cladding layer3107 made of In(x′″)Ga(y′″)Al(1−x″−y″)P, an n-type GaAs contact layer3108, an ITO (Indium Tin Oxide) transparent electrode 3109, and abonding Cr/An electrode 3110 are sequentially formed on the uppersurface of a p-type silicon substrate 3101. A p-type electrode 3111 isformed on the lower surface of the substrate 3101. A voltage is appliedbetween the electrodes 3110 and 3111 to supply power to thelight-emitting element and emit light from the active layer 3106.

In this structure, part of light that is emitted upward in FIG. 1 by theactive layer 3106 passes through the transparent cladding layer 3107 andthin-film GaAs contact layer 3108. The light further passes through thetransparent electrode 3109 and radiates outside.

Light emitted downward by the active layer 3106 passes through thecladding layer 3105 and thin-film contact layer 3104. The light isreflected by the electrode 3103 functioning as a reflective layer,radiated to above the element, and extracted outside.

Since the electrode 3103 is made of a metal, unlike a conventionalreflective layer, the electrode 3103 hardly changes in reflectivity withrespect to the incident angle, and reflects almost all light. Thus,light can be efficiently extracted.

If the n- and p-type contact layers are made of InGaP or InGaAlP, theband gap difference between each contact layer and the correspondingcladding layer decreases to further reduce the operating voltage.

Since the metal electrode 3110 is formed on the upper surface of thetransparent electrode 3109, stress strain applied to the active layer3106 by the transparent electrode 3109 can be relaxed to improve thereliability.

If the p-type electrode 3103 has a layered structure of a transparentconductive layer and a metal containing Al or Ag, the reflectivity canbe increased to increase the light output from the light-emittingelement.

(2) The Second Embodiment

The second embodiment of the present invention will be described withreference to FIG. 2. An SnPb solder layer 3302, a p-type Au/Zn electrode3303, a p-type GaAs contact layer 3304 having a thickness of 500 Å and acarrier concentration of 1E19 cm⁻³, a p-type cladding layer 3305 made ofIn(x′)Ga(y′)Al(1−x′−y′)P(0=<(x′,y′)=<1) with a thickness of 2 μm and acarrier concentration of 5E18 cm⁻³, an active layer 3306 made ofIn(x″)Ga(y″)Al(1−x″−y″)P(0=<(x″,y″)=<1), an n-type cladding layer 3307made of In(x′″)Ga(y′″)Al(1−x′″−y′″)P(0=<(x′″,y′″)=<1) with a thicknessof 1.5 μm and a carrier concentration of 3E18 cm⁻³, an n-type GaAscontact layer 3308 having a thickness of 500 Å and a carrierconcentration of 1E19 cm⁻³, an ITO (Indium Tin Oxide) transparentelectrode 3309, and a bonding Cr/An electrode 3310 are formed on theupper surface of an Al substrate 3301.

In the structure of the second embodiment, a light-emitting layer with adouble-heterostructure made up of the active layer 3306 and claddinglayers 3305 and 3307 is formed on the Al substrate 3301. Heat generatedin the active layer 3306 dissipates via the Al substrate 3301. As aresult, the semiconductor light-emitting element can operate withoutdecreasing the light output even at a high temperature of 100° C.

In this case, the compositions (x′, x′″, y′, y′″) of the cladding layers3305 and 3307 and the composition (x″, y″) of the active layer 3306 areadjusted such that the band gaps of the cladding layers 3305 and 3307become larger than that of the active layer 3306. This enables settingsufficiently high densities of electrons and holes contributing toemission, increasing the light output. If the active layer 3306 isformed into a single or multiple quantum well structure made up of awell layer several ten Å thick and a barrier layer several ten Å thick,a large light output can be obtained with a small current. By changingthe composition of the active layer 3306, the semiconductorlight-emitting element can emit light from red to green. If the n- andp-type contact layers are made of InGaP or InGaAlP, light can beextracted without being absorbed by the contact layers.

(3) The Third embodiment

The third embodiment of the present invention will be described withreference to FIG. 3. N-type Au/Ge electrodes 3411 and 3402 arerespectively formed on the lower and upper surfaces of an n-type siliconsubstrate 3401. A p-type Au/Ni/Au electrode 3403, a p-type GaN contactlayer 3404, a p-type AlGaN cladding layer 3405, an InGaN active layer3406, an n-type AlGaN cladding layer 3407, an n-type GaN contact layer3408, an ITO transparent electrode 3409, and a bonding Cr/An electrode3410 are formed on the surface of the n-type electrode 3402.

According to this embodiment, a current can be spread by the ITOtransparent electrode 3409 and injected to the entire active layer 3406to cause the entire region of the active layer 3406 to emit light. Lightemitted upward by the active layer 3406 passes through the transparentcladding layer 407, further passes through the contact layer 408 andelectrode 3409, and radiates outside. Light emitted downward by theactive layer 3406 passes through the cladding layer 3405 and contactlayer 3404. Then, all the light is reflected by the p-type electrode3403, radiated upward, and extracted outside.

Since the electrode 3403 serving as a reflective layer is made of ametal, the electrode 3403 reflects all light without absorbing it, andthe light can be efficiently extracted outside. If the electrode 3403 ismade of a metal containing Al or Ag, its reflectivity can be increasedto increase light output.

The cladding layer may be made of In(x1)Ga(y1)Al(1−x1−y1)N, and the bandgap can be controlled by changing the compositions x1 and y1. Similarly,the active layer 3406 may be made of In(x2)Ga(y2)Al(1−x2−y2)N, andemission from infrared radiation to ultraviolet radiation can berealized by changing the compositions x2 and y2. If the cladding andactive layers have the same lattice constant, high luminance can berealized with a small current. For ultraviolet radiation, the ITOtransparent electrode 3409 is made as thin as several hundred Å or usesa thin metal film several 10 Å thick, thereby increasing light output.

(4) The Fourth Embodiment

A method of manufacturing the semiconductor light-emitting element ofthe first embodiment will be explained as the fourth embodiment of thepresent invention with reference to FIGS. 4 to 8.

As shown in FIG. 4, a GaAs buffer layer 3011, an InGaAlP selectiveetching layer 3012, an n-type GaAs contact layer 3108, an n-type InGaAlPcladding layer 3107, an InGaAlP active layer 3106, an InGaAlP claddinglayer 3105, and a p-type GaAs contact layer 3104 are sequentially grownon a GaAs substrate 3010 using MOCVD or MBE.

As shown in FIG. 5, a p-type electrode 3103 is formed on the surface ofthe contact layer 3104, and adhered via a solder layer 3013 of SnPb orthe like to a p-type silicon substrate 3101 having p-type electrodes3102 and 3111 formed on its lower and upper surfaces.

After the end face of the wafer is covered with wax except for theselective etching layer 3012, the selective etching layer 3012 is etchedaway with phosphoric acid or sulfuric acid, as shown in FIG. 6. In thiscase, heating the phosphoric acid or sulfuric acid to a high temperaturefacilitates removal by etching.

As shown in FIG. 7, a transparent electrode 3109 and bonding electrode3110 are formed on the surface of the contact layer 3108. The resultantwafer is divided into a plurality of chips by scribing or dicing.

As shown in FIG. 8, an LED chip 2 is placed on a frame 1 or substrateusing Ag paste 4 or the like, and bonded to the frame 1 or substrateusing an Au wire 3. Then, a resin mold 5 is formed to cover the LED chip2 and Au wire 3.

The above-described embodiments are merely examples, and do not limitthe present invention. The substrate may be a p- or n-type siliconsubstrate, like the first and third embodiments, or may be made of ametal such as Al, like the second embodiment. The metal is not limitedto Al, and may be Cu, Fe, or stainless steel.

A substrate made of such metal exhibits a large heat dissipation effect.Hence, even when a large current of several 10 A flows, saturation oflight output by heat generation does not occur, and the semiconductorlight-emitting element can operate even at a temperature of 100° C.

(5) The Fifth Embodiment

In the first embodiment, the electrodes 3102 and 3103 directly contacteach other. Alternatively, like the fifth embodiment shown in FIG. 9, anintermediate layer 3120 made of In, Ag, Ni, Cr, or the like may besandwiched between the electrodes 3102 and 3103. In this case, thermalstrain of the active layer can be reduced to improve the reliability.

(6) The Sixth Embodiment

In the first embodiment, the p-type contact layer 3104 and p-typecladding layer 3105 directly contact each other. Alternatively, like thesixth embodiment shown in FIG. 10, a strain relaxing layer may besandwiched between the p-type contact layer 3104 and the p-type claddinglayer 3105. This structure can prevent dislocations from theheterojunction caused by current injection. Doping In into the strainrelaxing layer can soften the crystal structure and suppress an increasein dislocations.

(7) The Seventh Embodiment

FIG. 11 shows the structure of a semiconductor light-emitting elementaccording to the seventh embodiment of the present invention.

An In(x1)Ga(y1)Al(1−x1−y1)P buffer layer 101, n-typeIn(x2)Ga(y2)Al(1−x2−y2)P contact layer 102, n-typeIn(x3)Ga(y3)Al(1−x3−y3)P cladding layer 103, In(x4)Ga(y4)Al(1−x4−y4)Pactive layer 104, p-type In(x5)Ga(y5)Al(1−x5−y5)P cladding layer 105,and p-type In(x6)Ga(y6)Al(1−x6−y6)P contact layer 106 are sequentiallyformed on a transparent ZnSe semiconductor substrate 100.

An n-type AuGe electrode 107 is formed on the partially etched n-typecontact layer 102, whereas a p-type AuZn electrode 108 is formed on thep-type contact layer 106. In this case, 0<=x1, . . . , x6, y1, . . . ,y6, x1+y1, . . . , x6+y6<=1.

The electrode material can desirably ohmic-contact the contact layer,and exhibit a high light reflectivity.

Light emitted by the active layer 104 is extracted outside via thesemiconductor substrate 100. Light traveling toward the p-type electrode108 is reflected by the electrode 108, and extracted outside via thesubstrate 100. Since no obstacle exists on the light extraction surface,light inside the element can be effectively extracted to increase thelight extraction efficiency.

ZnSe used for the substrate 100 has a lattice constant of 5.667 Å. Thislattice constant can be controlled from 5.451 Å to 5.868 Å by changingthe compositions x and y of the In(x)Ga(y)Al(1−x−y)P layer formed on thesubstrate 100. Thus, the light-emitting layer 104 which islattice-matched with the ZnSe substrate 100 or is not lattice-matchedbut has a thickness falling within the critical film thickness can beformed with high crystallinity.

The compositions of the cladding layer 103 and contact layer 106 areadjusted to be larger than the band gap of the active layer 104. Thiscan realize a structure free from any internal absorption.

By changing the composition of the active layer 104, light ranging fromred to green can be emitted. If the active layer 104 is formed into asingle or multiple quantum well structure using a quantum well layerseveral ten Å thick, high emission efficiency and long service life canbe attained.

The n-type electrode 107 is formed by ion-implanting or diffusing ann-type impurity in the p-type contact layer 106. The p- and n-typeelectrodes 108 and 107 are formed on the same plane. This enablesdirectly adhering the p-type electrode 108 to a heat sink. Since heatcan satisfactorily dissipate, the semiconductor light-emitting elementcan operate up to a large current of several A without saturating alight output.

(8) The Eighth Embodiment

FIG. 12 shows the structure of a semiconductor light-emitting elementaccording to the eighth embodiment of the present invention.

An In(x1)Ga(y1)Al(1−x1−y1)P buffer layer 201, n-typeIn(x2)Ga(y2)Al(1−x2−y2)P contact layer 202, n-typeIn(x3)Ga(y3)Al(1−x3−y3)P cladding layer 203, In(x4)Ga(y4)Al(1−x4−y4)Pactive layer 204, p-type In(x5)Ga(y5)Al(1−x5−y5)P cladding layer 205,and p-type In(x6)Ga(y6)Al(1−x6−y6)P contact layer 206 are sequentiallyformed on a GaAs semiconductor substrate 200.

An n-type AuGe electrode 207 is formed on the partially etched n-typecontact layer 202, whereas a p-type AuZn electrode 208 is formed on thep-type contact layer 206.

A light extraction window 209 is formed in the substrate 200 at aposition where the light extraction window 209 faces the p-typeelectrode 208 via the active layer 204 so as to extract light. In thiscase, 0<=x1, . . . , x6, y1, . . . , y6, x1+y1, . . . , x6+y6<=1.

Light emitted by the active layer 204 is extracted outside via the lightextraction window 209. Light traveling toward the p-type electrode 208is reflected by the electrode 208, and extracted outside via the window209.

As for the size of the electrode 208, if the electrode 208 is largerthan the light extraction window 209, part of light is absorbed by thesubstrate 200, and cannot be sufficiently extracted. Thus, the electrode208 is desirably smaller than the light extraction window 209. Sincelight emitted by the active layer 204 can be effectively extracted, alight output from the element increases.

The eighth embodiment can effectively extract internal light because noobstacle exists on the light extraction surface. The compositions of thecladding layers 203 and 205 and contact layers 202 and 206 are adjustedto be larger than the band gap of the active layer 204. This can realizea structure free from any internal absorption.

By changing the composition of the active layer 204, light ranging fromred to green can be emitted.

If the active layer 204 is formed into a single or multiple quantum wellstructure using a quantum well layer several ten Å thick, high emissionefficiency and long service life can be attained.

The n-type electrode 207 is formed on the same plane as the p-typeelectrode 208 by forming a region in which an n-type impurity ision-implanted or diffused from the p-type contact layer 206. Thisenables directly adhering the p-type electrode 208 to a heat sink, sothat the semiconductor light-emitting element can operate up to a largecurrent of several Å without saturating a light output.

(9) The Ninth Embodiment

FIG. 13 shows the structure of an element according to the ninthembodiment of the present invention.

An n-type In(x1)Ga(y1)Al(1−x1−y1)P buffer layer 301, n-typeIn(x2)Ga(y2)Al(1−x2−y2)P cladding layer 302, n-typeIn(x3)Ga(y3)Al(1−x3−y3)P active layer 303, p-typeIn(x4)Ga(y4)Al(1−x4−y4)P cladding layer 304, and p-typeIn(x5)Ga(y5)Al(1−x5−y5)P contact layer 305 are sequentially formed onthe upper surface of an n-type GaP substrate 300. An n-type AuGeNielectrode 306 is formed on the lower surface of the n-type GaP substrate300. A light extraction window 308 is formed in the n-type electrode306. A p-type AuZn electrode 307 is formed on the p-type contact layer305 whose surface is etched into a recessed shape.

In this case, xa+ya<=1, 0<=xa, ya<=1, and a=1 to 5.

Light emitted by the active layer 303 travels straight in a directionindicated by an arrow A, and is extracted outside the element via thelight extraction window 308 on the n-type electrode 306 side. Lightindicated by an arrow B is reflected by the p-type electrode 307 formedon the recessed surface of the contact layer 305, and extracted outsidefrom the side surface.

In the element shown in FIG. 27, light reflected by the p-type electrode1107 is further reflected by the n-type electrode 1100, absorbed by theinternal impurity of the crystal, converted into heat,and thus cannot beextracted outside. This embodiment, however, can effectively extractsuch light outside the element to increase the light extractionefficiency.

The compositions of the cladding layers 302 and 304 and contact layer305 are adjusted to be larger than the band gap of the active layer 303.This can realize a structure free from any internal absorption.

By changing the composition of the active layer 303, light ranging fromred to green can be emitted.

If the active layer 303 is formed into a single or multiple quantum wellstructure using a quantum well layer several ten Å thick, high emissionefficiency and long service life can be attained.

(10) The 10th Embodiment

The 10th embodiment of the present invention will be described withreference to FIG. 14. This embodiment uses ZnSe for a semiconductorsubstrate.

An n-type In(x1)Ga(y1)Al(1−x1−y1)P buffer layer 401 which islattice-matched with a substrate 400, n-type In(x2)Ga(y2)Al(1−x2−y2)Pcladding layer 402, In(x3)Ga(y3)Al(1−x3−y3)P active layer 403, p-typeIn(x4)Ga(y4)Al(1−x4−y4)P cladding layer 404, and p-typeIn(x5)Ga(y5)Al(1−x5−y5)P contact layer 405 are sequentially formed onthe upper surface of the n-type ZnSe substrate 400.

An n-type AuGeNi electrode 406 is formed on the lower surface of then-type ZnSe substrate 400, whereas a p-type AuZn electrode 407 is formedon the partially etched p-type contact layer 405.

The compositions x1 to x5 and y1 to y5 of the respective layers 401 to405 must be adjusted within a range in which these layers 401 to 405 canbe lattice-matched with the n-type ZnSe substrate 400. The band gaps ofthe p- and n-type cladding layers 404 and 402 are set larger than thatof the active layer 403 to enhance the double-hetero effect.

In this structure, similar to the ninth embodiment, the surface of thep-type contact layer 405 is etched into a recessed shape. Light emittedby the active layer 403 can be reflected below the p-type electrode 407and extracted from the end face, so that the extraction efficiencyincreases.

As for the element size, a general element has a size of 300 μm×300 μm.In the 10th embodiment, the element has a size of 100 μm×100 μm, whichcan reduce light absorption inside the element to increase the lightextraction efficiency. More specifically, a light output from the entireelement is substantially doubled.

By changing the compositions x3 and y3 of the active layer 403, lightranging from red to green can be emitted. If the active layer 403 isformed into a quantum well structure about several ten Å in elementthickness, the stress by the ZnSe substrate can be reduced to achievelong service life.

(11) The 11th Embodiment

FIG. 15 shows a structure according to the 11th embodiment according tothe present invention.

An n-type In(x1)Ga(y1)Al(1−x1−y1)P buffer layer 501, n-typeIn(x2)Ga(y2)Al(1−x2−y2)P cladding layer 502, In(x3)Ga(y3)Al(1−x3−y3)Pactive layer 503, p-type In(x4)Ga(y4)Al(1−x4−y4)P cladding layer 504,and p-type In(x5)Ga(y5)Al(1−x5−y5)P contact layer 505 are sequentiallyformed on the upper surface of an n-type GaP semiconductor substrate500.

An n-type AuGeNi electrode 506 is formed on the lower surface of then-type GaP substrate 500, whereas a p-type AuZn electrode 507 is formedon the p-type contact layer 505.

In this case, xa+ya<1, 0<=xa, ya<=1, and a=1 to 5.

As the element shape, the element is processed into an octagonal prismwhose surface is octagonal, as shown in FIG. 15. Light, which isradiated to the four corners of a general element having a quadrangularprism shape whose surface is quadrangular, can be extracted outsidewithout being completely reflected because the four corners of theelement are cut.

The element shape is not limited to the octagonal shape, and may be apolygonal shape having five or more corners. As the number of cornersincreases, the light extraction efficiency increases. If the elementshape is a circular cylinder whose surface is circular, the lightextraction efficiency further increases.

The compositions of the cladding layers 502 and 504 and contact layer505 are adjusted to be larger than the band gap of the active layer 503,which can realize a structure free from any internal absorption. Bychanging the composition of the active layer 503, light ranging from redto green can be emitted.

If the active layer 503 is formed into a single or multiple quantum wellstructure using a quantum well layer several ten Å thick, high emissionefficiency and long service life can be attained.

(12) The 12th Embodiment

FIG. 16 shows the 12th embodiment of the present invention.

An n-type In(x1)Ga(y1)Al(1−x1−y1)N buffer layer 601, n-typeIn(x2)Ga(y2)Al(1−x2−y2)N cladding layer 602, In(x3)Ga(y3)Al(1−x3−y3)Nactive layer 603, p-type In(x4)Ga(y4)Al(1−x4−y4)N cladding layer 604,and p-type In(x5)Ga(y5)Al(1−x5−y5)N contact layer 605 are sequentiallyformed on the upper surface of an n-type GaN substrate 600.

An n-type TiAu electrode 606 is formed on the lower surface of then-type GaN substrate 600, while a p-type NiAu electrode 607 is formed onthe p-type contact layer 605.

In this case, xa+ya<=1, 0<=xa, ya<=1, and a=1 to 5.

As shown in FIG. 15, the element is processed into an octagonal prismwhose surface is octagonal, thereby increasing the light extractionefficiency. The element shape is not limited to the octagonal shape, andmay be a polygonal shape having five or more corners. If the element isprocessed into a circular cylinder, as shown in FIG. 16, the lightextraction efficiency further increases.

The compositions of the cladding layers 602 and 604 and contact layer605 are adjusted to be larger than the band gap of the active layer 603.This realizes a structure free from any internal absorption.

By changing the composition of the active layer 603, light ranging fromred to green can be emitted.

If the active layer 603 is formed into a single or multiple quantum wellstructure using a quantum well layer several ten Å thick, high emissionefficiency and long service life can be attained.

(13) The 13th Embodiment

In recent years, so-called photonics crystals are being available. The“photonics crystal” is attained by imparting a periodic gradient indexto a medium. The effects of the photonics crystal become stronger fortwo and three dimensions, and exhibit characteristic optical properties.

The feature of the photonics crystal is based on the band gap. Since theband gap does not permit any optical state, light having a photon energycorresponding to the band gap cannot exist in the crystal. Thus,external light incident on the crystal is reflected. If a defect islinearly introduced into the crystal, photons are permitted to exist inthe crystal. This realizes the light confinement effect and waveguide.

An example of the photonics crystal is one using a wafer bondingtechnique that is described in the following reference by Noda et al.:

“the Journal of the Institute of Electronics, Information andCommunication Engineers, March 1999, pp. 232-241”

FIGS. 28A to 28E show the steps of the manufacturing method. As shown inFIG. 28A, an AlGaAs layer 1201 and GaAs layer 1202 are formed on a GaAssubstrate 1200.

As shown in FIG. 28B, the GaAs layer 1202 is patterned into a gratingshape.

The substrate processed in this manner, and another substrate made up ofa GaAs substrate 1210, AlGaAs layer 1211, and GaAs layer 1212 areprepared, and fused while being positioned to make the stripe-shapedGaAs layers 1202 and 1212 be perpendicular to each other, as shown inFIG. 28C.

As shown in FIG. 28D, one substrate 1210 and one AlGaAs layer 1211 areselectively etched with an etchant.

By repeating the steps in FIGS. 28A to 28D, a photonics crystal withdiffraction gratings made up of the GaAs-based semiconductor materialand the air is manufactured. In this case, every second diffractiongratings parallel to each other must be shifted in phase by half theperiod of emitted light.

The 13th embodiment of the present invention using this photonicscrystal will be explained with reference to FIGS. 17A and 17B.

As shown in FIG. 17A, a p-type GaAs buffer layer 701, p-type GaAscontact layer 712, p-type InGaAlP cladding layer 702, InGaAlP activelayer 703, and n-type InGaAlP cladding layer 704 are sequentially grownon a p-type GaAs substrate 700 by MOCVD.

Separately from this structure, a photonics crystal layer 705 isprepared through the above-described steps, and fused onto the n-typeInGaAlP cladding layer 704. An n-type GaAs n-type GaAs layer 706 isformed on the photonics crystal layer 705.

The p-type GaAs substrate 700 and p-type GaAs buffer layer 701 areremoved. As shown in FIG. 17B, an n-type electrode 708 is formed on then-type GaAs layer 706, and a p-type transparent electrode 709 is formedon the p-type GaAs contact layer 712. The p-type transparent electrode709 is partially removed to form a blocking layer 711. A p-typeelectrode pad 710 is formed from the p-type transparent electrode 709 tothe blocking layer 711.

In this structure, light emitted by widening a current flowing from thep-type electrode pad 710 by the p-type transparent electrode 709 andinjecting it into the active layer 703 is reflected by the photonicscrystal layer 705, and extracted via the p-type transparent electrode709.

The photonics crystal layer 705 reflects 90% or more of light. As aresult, a light output of 8 mW with an emission wavelength of 630 nm canbe obtained for a current value of 20 mA. This value is about double thevalue of the element shown in FIG. 27, and the light extractionefficiency greatly increases.

(14) The 14th Embodiment

The structure of an element according to the 14th embodiment of thepresent invention will be described with reference to FIG. 18.

The 14th embodiment concerns a GaN-based compound semiconductorlight-emitting element in which a photonics crystal having a throughdislocation is formed on the light extraction surface.

A GaN buffer layer (not shown), n-type GaN layer 802, n-type AlGaNcladding layer 803, InGaN active layer 804, p-type AlGaN cladding layer805, and p-type GaN contact layer 809 are sequentially grown on asapphire substrate 801.

The p-type AlGaN cladding layer 805, InGaN active layer 804, and n-typeAlGaN cladding layer 803 are partially etched to expose the surface ofthe n-type GaN layer 802. A p-side electrode & bonding electrode 806(which need not be transparent) is formed on the p-type GaN contactlayer 809, and an n-side electrode 807 is formed on the n-type GaN layer802.

Separately from this structure, e.g., a GaN photonics crystal layer isformed on a sapphire substrate. GaN on the sapphire substrate containsmany through dislocations. Such a photonics crystal layer 808 and thesapphire substrate 801 are fused. In this case, the sapphire substrate801 is transparent and does not absorb emitted light.

In this structure, a current flowing from the p-side electrode 806 isinjected from the p-type GaN contact layer 809 to the InGaN active layer804 to emit light. The light is extracted outside the element via thephotonics crystal layer 808.

As described above, the photonics crystal layer 808 contains manythrough dislocations. Thus, the photonics crystal layer 808 does notreflect light, unlike the n-type GaAs layer 706 in the 13th embodiment,and light travels along the through dislocations and is efficientlyextracted outside the chip. This photonics crystal layer 808 alsofunctions as a filter to obtain monochrome light with a smallerhalf-width wavelength.

(15) The 15th Embodiment

The 15th embodiment will be described with reference to FIG. 19. Thisembodiment concerns an example in which no photonics crystal isintroduced.

The 15th embodiment is about a GaN-based compound semiconductorlight-emitting element. A GaN buffer layer (not shown), n-type GaN layer902, n-type AlGaN cladding layer 903, InGaN active layer 904, p-typeAlGaN cladding layer 905, and p-type GaN contact layer 911 aresequentially grown on an n-type GaN substrate 901. The p-type GaNcontact layer 911, p-type AlGaN cladding layer 905, InGaN active layer904, n-type AlGaN cladding layer 903, and n-type GaN layer 902 arepartially etched to expose the surface of the n-type GaN layer 902.

A p-side transparent electrode 906 is formed on the p-type AlGaNcladding layer 905. A current blocking layer 907 made of a currentblocking insulating film is formed adjacent to the p-side transparentelectrode 906. A p-side bonding electrode 908 connected to the p-sidetransparent electrode 906 is formed on the current blocking layer 907.Further, an n-side electrode 910 is formed on the n-type GaN contactlayer 902.

After the interface of the n-type GaN layer 902 is corrugated, then-type AlGaN cladding layer 903 is grown to have the gradient index. Asa method of corrugating the interface of the n-type GaN layer 902, themethod shown in FIGS. 20A to 20D or FIGS. 21A to 21C may be employed.

According to the method shown in FIGS. 20A to 20D, a GaN buffer layer2001 and n-type GaN contact layer 2002 are sequentially formed on asapphire substrate 2000, as shown in FIG. 20A.

As shown in FIG. 20B, a resist is applied and patterned byphotolithography to form a resist film 2003.

As shown in FIG. 20C, the surface of the n-type GaN contact layer 2002is corrugated using the resist film 2003 as a mask.

As shown in FIG. 20D, a p-type AlGaN cladding layer 2003 is formed toplanarize the surface.

Alternatively, according to the method shown in FIGS. 21A to 21C, a GaNbuffer layer 2101 and n-type GaN contact layer 2102 are sequentiallyformed on a sapphire substrate 2100, as shown in FIG. 21A.

As shown in FIG. 21B, the ratio of Cl₂ gas is set high by setting theratio of an etching gas flow rate in reactive ion etching toBC₁₃:Cl₂=1:1. Then, the surface of the n-type GaN contact layer 2102becomes rough.

As shown in FIG. 21C, a p-type AlGaN cladding layer 2103 is formed toplanarize the surface.

According to the 15th embodiment, the interface of the n-type GaN layer902 is corrugated to have the gradient index with the n-type AlGaNcladding layer 903. Light is reflected and scattered by the interface,and a larger amount of light is extracted outside the element.

(16) The 16th Embodiment

An element according to the 16th embodiment will be explained withreference to FIGS. 22A to 22D. As shown in FIG. 22A, a buffer layer (notshown), cladding layer 2201, active layer 2202, and cladding layer 2203are sequentially formed on a substrate 2200. A resist film 2204 isformed on a surface of the substrate 2200 opposite to the elementformation surface.

As shown in FIG. 22B, the resist film 2204 is heated to round its edge.

As shown in FIG. 22C, the structure is etched using the resist film 2204as a mask to process the edge of the semiconductor substrate 2200 into ashape corresponding to the rounded shape of the resist film 2204.

As shown in FIG. 22D, a photonics crystal layer 2204 having a highreflectivity is fused to the substrate 2200.

According to the 16th embodiment, as indicated by arrows in FIG. 22D,light emitted by the active layer 2202 is reflected by the etchedportions of the substrate 2200 at various angles. Accordingly, the lightextraction efficiency and emission intensity increase.

(17) The 17th Embodiment

A light-emitting element which emits light with three wavelengths can beimplemented by forming, on a photonics crystal layer, threelight-emitting elements having different emission wavelengths like alight-emitting element formed on a sapphire substrate.

As shown in FIG. 23, blue- and green-emitting elements 2302 and 2303 areformed on one surface of a photonics crystal layer 2300, while ared-emitting element 2301 is formed on the other surface.

The photonics crystal layer 2300 having a high reflectivity with respectto light in the short-wave range is formed to prevent short-wavelengthbeams from the blue- and green-emitting elements 2302 and 2303 frompassing through the photonics crystal layer 2300 and optically excitingthe active layer of the red-emitting element 2301. The red-emittingelement 2301 for emitting a long-wavelength beam is fused to the lowersurface of the photonics crystal layer 2300. With this structure, blue,green, and red beams are mixed to obtain a white beam.

In this case, the colors of light-emitting elements can be variouslycombined, and the mixed color is changed in accordance with thecombination.

(18) The 18th Embodiment

The 18th embodiment of the present invention will be described withreference to FIG. 24. This embodiment exemplifies a GaN-based RC-LED(Resonance Cavity LED). An n-type GaN buffer layer 2401, and AlGaN/GaNDBR (Distributed Bragg Reflector) layer 2402 having a mediumreflectivity are formed on a transparent GaN-based semiconductorsubstrate 2400. Further, an InGaN active layer 2403 having a MQW(Multiple Quantum Well) structure, p-type AlGaN cladding layer 2404, andp-type InGaN bonding layer 2405 are formed on the DBR layer 2402.

A photonics crystal layer 2406 with a high reflectivity that is preparedseparately is bonded to the cladding layer 2404 via the bonding layer2405. Then, a p-type electrode 2407 is formed on the lower surface ofthe photonics crystal layer 2406, and an n-type electrode 2408 is formedon the upper surface of the semiconductor substrate 2400.

The DBR layer having a high reflectivity is difficult to obtain using aGaN-based semiconductor material. By introducing the photonics crystallayer 2406, high light extraction efficiency can be realized.

The materials of the respective layers are not limited to the aboveones, and another GaN-based semiconductor material or a GaAs-basedsemiconductor material may be adopted. If a GaAs-based material isadopted, GaAs absorbs emitted light. To prevent this, the substrate isremoved to fuse the light-emitting layer to a GaP substrate or the like.

The element according to the 18th embodiment can also be applied to aVCSEL (Vertical Cavity Surface Emitting Laser).

A method of forming a GaN-based photonics crystal will be described withreference to FIGS. 25A to 25E.

As shown in FIG. 25A, a buffer layer 2501 and In(x)Al(y)Ga(1−x−y)N layer(0≦x, y≦1) 2502 are formed on a GaN substrate 2500.

As shown in FIG. 25B, the In(x)Al(y)Ga(1−x−y)N layer 2502 is patternedinto a grating shape.

The substrate processed in this manner, and another substrate made up ofa GaN substrate 2600, buffer layer 2601, and In(x)Al(y)Ga(1−x−y)N layer2602 are prepared, and fused while being positioned to make thestripe-shaped layers 2502 and 2602 be perpendicular to each other, asshown in FIG. 25C.

As shown in FIG. 25D, one GaN substrate 2600 is removed by irradiatingit with a laser beam.

As shown in FIG. 25E, the buffer layer 2601 is removed by reactive ionetching.

By repeating the steps in FIGS. 25A to 25E, a photonics crystal havingdiffraction gratings is manufactured. In this case, every seconddiffraction gratings parallel to each other must be shifted in phase byhalf the period of emitted light.

According to the 13th to 18th embodiments, a photonics crystal region ora region having a predetermined gradient index is formed on at least onesurface of the light-emitting layer of a compound semiconductorlight-emitting element.

In particularly, the photonics crystal does not permit lightcorresponding to the band gap to exist, and thus functions as ahigh-reflectivity film. The photonics crystal exhibits a highreflectivity with respect to a light component other than a verticallyincident light component. By introducing this photonics crystal as areflective layer, the light extraction efficiency can be increased.

In a GaN-based compound semiconductor light-emitting element, manythrough dislocations exist in a GaN layer. When a photonics crystal isformed using this crystal, the photonics crystal fused to the substratecontains many through dislocations. Hence, light travels along thedislocations and is efficiently extracted outside the element. Thephotonics crystal in this case functions as a filter, so that monochromelight with a smaller half-width wavelength can be obtained.

If a light-emitting element having a different emission wavelength fromthat of a light-emitting element formed on a sapphire substrate isformed on a photonics crystal layer, a light-emitting element foremitting light with two wavelengths can be implemented.

Alternatively, the interface of a semiconductor layer is corrugated toobtain the gradient index inside the semiconductor layer. Light isreflected and scattered by this interface, and can be more effectivelyextracted outside the element.

The gradient index may be obtained inside the semiconductor layer by acombination of semiconductor layers having different refractive indices.

In a gradient index region, light emitted by an active layer isreflected by a larger amount in a chip, and extracted from the lightextraction surface. This can greatly increase the light extractionefficiency and luminance.

The increase in luminance can decrease the injection current and canalso improve the element reliability.

1-14. (Cancelled)
 15. A semiconductor light-emitting elementmanufacturing method comprising the steps of: forming a buffer layer ona transparent semiconductor substrate so as to be lattice-matched withthe semiconductor substrate; sequentially forming a first contact layer,a first cladding layer, a light-emitting layer, a second cladding layer,and a second contact layer on the buffer layer; partially removing thefirst cladding layer, the light-emitting layer, the second claddinglayer, and the second contact layer to expose a surface of the firstcontact layer; forming a first electrode on the exposed surface of thefirst contact layer; and forming a second light-reflecting electrode ona surface of the second contact layer.
 16. A semiconductorlight-emitting element manufacturing method comprising the steps of:sequentially forming a buffer layer, a first contact layer, a firstcladding layer, a light-emitting layer, a second cladding layer, and asecond contact layer on a semiconductor substrate; partially removingthe first cladding layer, the light-emitting layer, the second claddinglayer, and the second contact layer to expose a surface of the firstcontact layer; forming a first electrode on the exposed surface of thefirst contact layer; forming a second light-reflecting electrode on asurface of the second contact layer; and forming a light extractionwindow at a portion of the semiconductor substrate at which the lightextraction window faces the second electrode.
 17. (Cancelled)
 18. Asemiconductor light-emitting element manufacturing method comprising thesteps of: sequentially forming a buffer layer, a first cladding layer, alight-emitting layer, a second cladding layer, and a contact layer on atransparent semiconductor substrate; recessing a surface of the contactlayer; forming a first light-reflecting electrode on the surface of thecontact layer; and forming a second electrode on a surface of thesemiconductor substrate so as to remove a portion at which the secondelectrode faces the first electrode.
 19. A semiconductor light-emittingelement manufacturing method comprising the steps of: forming a bufferlayer on a transparent semiconductor substrate so as to belattice-matched with the semiconductor substrate; sequentially forming afirst cladding layer; a light-emitting layer, a second cladding layer,and a contact layer on the buffer layer; recessing a surface of thecontact layer; forming a first light-reflecting electrode on the surfaceof the contact layer; and forming a second electrode on a surface of thesemiconductor substrate. 20-27. (Cancelled)
 28. A semiconductorlight-emitting element manufacturing method comprising the steps of:sequentially forming a buffer layer, a first cladding layer, alight-emitting layer, and a second cladding layer on a firstsemiconductor substrate; forming a photonics crystal layer on a secondsemiconductor substrate; fusing the second cladding layer and thephotonics crystal layer; and removing the first semiconductor substrateand the buffer layer.
 29. A semiconductor light-emitting elementmanufacturing method comprising the steps of: sequentially forming abuffer layer, a contact layer, a first cladding layer, a light-emittinglayer, and a second cladding layer on a first transparent semiconductorsubstrate; forming a photonics crystal layer on a second semiconductorsubstrate; fusing the first semiconductor substrate and the photonicscrystal layer; and removing the second semiconductor substrate, when thephotonics crystal layer contains a through dislocation on a lightextraction surface in a substantially vertical direction to pass lightemitted by the light-emitting layer.
 30. A semiconductor light-emittingelement manufacturing method comprising the steps of: forming a contactlayer on a semiconductor substrate; corrugating a surface of the contactlayer; and sequentially forming a first cladding layer, a light-emittinglayer, and a second cladding layer on the contact layer, wherein agradient index is given by the corrugated interface of the contact layerin contact with a first cladding layer, and light emitted by thelight-emitting layer is reflected by the interface.
 31. A semiconductorlight-emitting element manufacturing method comprising the steps of:forming at least a light-emitting layer on a semiconductor substrate;and processing an edge of the semiconductor substrate to round the edge.32. A semiconductor light-emitting element manufacturing methodcomprising the steps of: forming a buffer layer on a first transparentsemiconductor substrate; forming a Bragg reflective layer on the bufferlayer; sequentially forming a light-emitting layer, a cladding layer,and a bonding layer on the Bragg reflective layer; forming a photonicscrystal layer on a second semiconductor substrate; bonding the claddinglayer and photonics crystal layer via the bonding layer; and removingthe second semiconductor substrate.